Fuel tank and method for reducing vapor permeation through a fuel tank

ABSTRACT

A method of reducing fuel vapor permeation through a multi-layer tank includes providing a multi-layer overlay onto at least a portion of a structural layer of the multi-layer tank. The multi-layer overlay preferably comprises at least one structural layer composed of a polymeric material that is compatible with one or more of the polymeric structural layer(s) of the multi-layer tank. The multi-layer overlay further comprises at least one barrier layer composed of a vapor barrier material resistant to hydrocarbon permeation therethrough. The multi-layer overlay may be secured to the multi-layer tank by, for example, applying a suitable amount of heat and pressure thereto or by molding the multi-layer overlay to the tank body during a tank forming process.

REFERENCE TO RELATED APPLICATION

This application is a division of copending U.S. patent application Ser.No. 11/134,486, filed May 20, 2005. Applicants claim priority ofapplication Ser. No. 11/134,486 and provisional patent application Ser.No. 60/576,977, filed Jun. 4, 2004.

FIELD OF THE INVENTION

The present invention relates generally to fuel tanks and, moreparticularly, to a method of reducing vapor permeation through amulti-layer fuel tank.

BACKGROUND OF THE INVENTION

Multi-layer polymeric fuel tanks are often used in the automotiveindustry because they are lighter in weight, have greater flexibilityand are cheaper to manufacture than fuel tanks made of metal.Multi-layer polymeric fuel tanks typically include a tank wall composedof at least two layers of a high density polyethylene (HDPE) structuralmaterial and an ethylene vinyl alcohol copolymer (EVOH) hydrocarbonvapor barrier layer disposed between them. The fuel tanks may bemanufactured by, for example, co-extruding the multiple layers into twosheets and vacuum forming each sheet to form two complementary sectionsor halves of the fuel tank, blow molding coextruded parisons into twoshell sections of the fuel tank, blow-molding a coextruded cylindricalparison, or other fuel tank manufacturing processes known in the art.Component parts of a fuel system, such as a spout, a fuel pump, a ventvalve, a weld cap and/or a fuel level sensor may be disposed in or onone or both sections of the tank, or may be disposed in or on one ormore openings in the parison. The molded halves of the fuel tank or theopenings in the parison may then be welded together and/or pinchedclosed. The welded junctures and the pinched regions form seams in thetank wall with a discontinuous EVOH barrier layer in those regions,thereby creating permeation windows through which fuel vapors pass moreeasily through the tank wall and to the atmosphere.

SUMMARY OF THE INVENTION

A method of reducing fuel and fuel vapor permeation through amulti-layer tank comprises providing a multi-layer overlay on apolymeric structural layer of the multi-layer tank and over at least aportion of a vapor permeable seam formed in the tank. The multi-layeroverlay comprises at least one barrier layer composed of a vapor barriermaterial that is resistant to vapor permeation therethrough. Themulti-layer overlay further comprises at least one structural layercomposed of a polymeric structural material that is compatible with oneor more of the polymeric structural layer(s) of the multi-layer tank.The multi-layer overlay may be secured to the polymeric structural layerof the multi-layer tank by applying pressure and heat thereto or bymolding the overlay to the tank surface during a tank forming process.

One presently preferred embodiment of a multi-layer fuel tank includes amulti-layer wall comprising at least one polymeric structural layer, atleast one seam formed in the multi-layer wall and a multi-layer overlaycarried by the multi-layer wall and disposed over at least a portion ofthe seam. The multi-layer overlay comprises at least one barrier layercomposed of a barrier material that is resistant to vapor permeationtherethrough. The multi-layer overlay further comprises at least onestructural layer composed of a polymeric structural material that iscompatible with an adjacent polymeric structural layer of themulti-layer tank.

Objects, features and advantages of this invention include providing afuel tank that has improved resistance to fuel and fuel vapor permeationtherethrough, is rugged, durable, of relatively simple design andeconomical manufacture, and a method of reducing fuel and fuel vaporpermeation through a fuel tank that is relatively simple, inexpensiveand efficient for the manufacture and production of fuel tanks.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of this invention willbe apparent from the following detailed description of the preferredembodiments and best mode, appended claims and accompanying drawings inwhich:

FIG. 1 is a perspective view of a portion of an assembled multi-layerfuel tank showing a component weld seam, a pinch seam and a surface ofthe fuel tank body partially sealed by portions of a multi-layeroverlay;

FIG. 2 is a fragmentary cross-sectional view taken generally along line2-2 of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view taken generally along line3-3 in FIG. 1;

FIG. 4 is a somewhat schematic view of the multi-layer overlay beingsecured to the fuel tank using a single compression roller and a hightemperature roller;

FIG. 5 is a somewhat schematic view of the multi-layer overlay beingsecured to the fuel tank using multiple compression rollers and hightemperature rollers;

FIG. 6 is a somewhat schematic view of the multi-layer overlay beingsecured to the fuel tank using compression rollers and an inductioncoil;

FIG. 7 is a somewhat schematic view of the multi-layer overlay beingsecured to the fuel tank using a heated platen;

FIG. 8 is a somewhat schematic view of the multi-layer overlay beingsecured to the fuel tank using a hot drop manifold and an injectionmolding apparatus;

FIG. 9 is a perspective view of a mold for molding a fuel tank shell orhalf, where the mold includes a cavity in which a die-cut piece of aflat overlay is placed within for molding the overlay to the surface ofthe fuel tank shell body during the fuel tank molding or formingprocess;

FIG. 10 is a perspective view of the formed fuel tank shell or halfhaving the multi-layer overlay of FIG. 9 molded to a surface thereof;

FIG. 11 is a perspective view of an alternate embodiment multi-layeroverlay die-cut to correspond or conform to a surface or surfaces of thefuel tank shell body during the fuel tank molding or forming process;

FIG. 12 is a perspective view of the multi-layer overlay of FIG. 11molded or formed onto the surface of the fuel tank shell;

FIG. 13 is a fragmentary cross-sectional view taken generally along line13-13 in FIG. 1 of a spout of the multi-layer polymeric fuel tank;

FIG. 14 is a fragmentary perspective view of a corner of the multi-layerfuel tank showing a portion of a convoluted pinch seam covered by amulti-layer overlay.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIG. 1-3 illustrate a fueltank assembly 10 comprising a fuel tank body 12 having a tank wall 26with two weld seams 14, 16, where vapor permeation through the tank wall26 is reduced by covering at least a portion of the fuel tank wall andthe weld seams 14, 16 with a nonpermeable multi-layer overlay 18. Themulti-layer overlay 18 includes a barrier material that prevents orsubstantially inhibits hydrocarbon fuel and fuel vapor permeationthrough the fuel tank wall, particularly through the seams 14, 16. Themulti-layer overlay 18 may be provided in the form of a tape, strip,sheet or any other suitable form, and can be cut or shaped into anydesired size and/or shape for covering any hydrocarbon permeable seam orsurface area formed in an area or region of the fuel tank assembly 10 orfor covering any desired surface area of the tank wall. The overlay 18may be secured to the tank body 12 by applying pressure and heat theretoor by molding the overlay 18 to the tank body 12 during the fuel tankmolding or forming process.

As shown in FIG. 1, the overlay 18 may be cut into a strip for sealingthe seam 14 which is a pinch seam fainted when two molded shells orhalves 20, 22 of the fuel tank body 12 were welded together. Also shownin FIG. 1, the overlay may be die-cut into a disc 18′ for sealing theseam 16, which is a circular component weld seam formed when a componentpart, such as a spout 24, is welded to the tank body 12. Also shown inFIG. 1, the overlay 18′ may be die-cut to cover a desired a surface areaof the fuel tank wall to provide an additional barrier to vaporpermeation through the tank wall. Of course, other vapor permeable areasmay be present in a fuel tank, including by way of example and withoutlimitation, pinch seams formed when blow molding a fuel tank from ahollow, cylindrical, multi-layer plastic parison.

The fuel tank body 12 comprises a tank wall 26 that preferably is madeof three or more co-extruded layers. As shown in FIG. 2, the fuel tankwall 26 is composed of five layers including a hydrocarbon barrier layer28 sandwiched between two structural layers; an outer-most structurallayer 30 and an inner-most structural layer 32. The barrier layer 28 hasan outer surface 34 that is adhered to an inner surface 36 of theouter-most structural layer 30 by a first bonding layer 38 composed ofan adhesive material. The barrier layer 28 further has an inner surface40 that is adhered to an outer surface 42 of the inner-most structurallayer 32 by a second bonding layer 44, also composed of an adhesivematerial. Use of the five-layer construction of the tank wall 26 ismerely for illustrative purposes in describing the method of the presentinvention, other multi-layer tank wall constructions and configurationsmay also be used in, by way of example, three, four or six-layer orother tank wall configurations.

The structural layers 30, 32 of the tank wall 26 are composed of asuitable polymeric material to provide structural integrity to the fueltank assembly 10. Typically, the tank wall of multi-layer fuel tanksincludes at least one structural layer, but more commonly, comprises twoor more structural layers. As shown in FIG. 2, the fuel tank wall 26comprises two structural layers 30, 32, one or both of which may beformed from treated recycled polymeric material consisting essentiallyof a mixture of waste and/or scrap material left over from themanufacture of previous fuel tanks. Such polymeric material is oftenreferred to as re-grind material. One or both structural layers 30, 32can also be formed from virgin high density polyethylene (HDPE). In somefuel tanks, an intermediate layer of re-grind or recycled material maybe used, for example, between an adhesive layer and one of the inner orouter structural layers providing a six-layer fuel tank construction.

Although the HDPE-containing structural layers 30, 32 are structurallysuitable for fuel tanks, they have very poor hydrocarbon permeation orvapor barrier properties. Thus, the barrier layer 28 is incorporatedinto the multi-layer structure of the tank wall 26 to prevent or greatlyinhibit hydrocarbon vapors from permeating through the tank wall 26.Since the preferred barrier material for the barrier layer 28 of themulti-layer fuel tank wall 26 is a relatively expensive ethylene vinylalcohol copolymer (EVOH), a very thin layer of this material isincorporated between the structural layers 30, 32 and is adhered to thestructural layers 30, 32 using an adhesive material that makes up thebonding layers 38, 44. Suitable adhesives for use in fuel tankconstruction include modified polyethylene materials or other adhesivesknown in the art.

As previously mentioned in conjunction with FIG. 1, the fuel tank body12 may be manufactured by welding together two pre-molded fuel tankshells or halves 20, 22. The fuel tank halves 20, 22 are each separatelymanufactured by first co-extruding the multiple layers of the fuel tankwall 26. Then each half 20, 22 is formed using a blow molding, a vacuumforming, or another suitable tank-forming method. Additional componentparts to complete the fuel tank assembly 10, such as the spout 24, afuel pump (not shown), a vent valve, a weld cap and/or a fuel levelsensor (all of which are not shown in FIG. 1), are then welded to orotherwise assembled or disposed in the appropriate areas either insideor outside the fuel tank body 12. Then the two halves 20, 22 of the tankbody 12 are connected together by joining peripheral edges of each half20, 22 and thermal welding them together. One or more welding cycles ofheat is preferably applied to the entire periphery of the joined edgesof the halves 20, 22 to thereby form the seam 14.

As shown in FIG. 3, the welded pinch seam 14 joins the outer-moststructural layer 30′ of the tank wall 26′ in the first half 20 of thetank body 12 to the outer-most structural layer 30″ of the tank wall 26″in the second half 22 of the tank body 12 to thereby form a single,continuous structural layer that becomes, as shown in FIG. 1, theouter-most structural layer 30 of the fuel tank wall 26. In referenceagain to FIG. 3, the barrier layers 28′, 28″ each located underneaththeir respective structural layers 30′, 30″ of the two halves 20, 22typically do not completely join together after welding the two halves20, 22 together, thereby leaving a gap or permeation window 48 along atleast a portion of the pinch seam 14. The size of the permeation window48 is exaggerated in FIG. 3, as are the thicknesses of the multiplelayers of the tank wall 26 and the overlay 18 for descriptive purposes.Typically, the permeation window 48 is quite small, but large enough topermit hydrocarbon vapors to permeate through the pinch seam 14 at asignificant rate. This is true, at least in part, for blow molded tanksformed from co-extrusion of a cylindrical parison. It should be noted,however, that for vacuum-formed tanks or tanks formed by joining two ormore sections together, the permeation window 48 may be much largerbecause the region between the barrier layers is larger. A method, aswill be described, is suitable for covering and/or sealing weld or pinchseams formed in the manufacture of fuel tanks, as well as coveringand/or sealing other portions of the fuel tank, including withoutlimitation, fuel tank areas having a gap in a barrier layer, or a thinbarrier layer, or otherwise as desired.

One presently preferred embodiment of a method of controlling vaporpermeation in a fuel tank includes applying a piece of the multi-layeroverlay 18 to the fuel tank body 12 along and over a vapor permeableseam, such as the pinch seam 14 or the component weld seam 16, as shownin FIG. 1, to thereby form a fuel and fuel vapor permeation seal. Asshown in FIG. 3, a piece of the multi-layer overlay 18 may include fivelayers including a vapor barrier layer 50 sandwiched between twostructural layers; an outer-most structural layer 52 and an inner-moststructural layer 54. This configuration is substantially similar to thefive-layer arrangement of the fuel tank wall 26 shown in FIG. 2. Asshown in FIG. 3, the barrier layer 50 includes an outer surface 56 thatis adhered to an inner surface 58 of the outer-most structural layer 52by a first bonding layer 60 composed of an adhesive material. Thebarrier layer 50 further includes an inner surface 62 that is adhered toan outer surface 64 of the inner-most structural layer 54 by a secondbonding layer 66, also composed of an adhesive material.

The barrier layer 50 of the multi-layer overlay 18 is preferablycomposed of EVOH or any other suitable hydrocarbon vapor barriermaterial. The structural layers 52, 54, may be composed of any number ofsuitable structural materials known in the art. The inner-moststructural layer 54 of the overlay 18 is preferably composed of astructural material that is compatible (e.g., weldable or bondable) withthe outer-most structural layer 30 of the fuel tank wall 26. Since thestructural material of the outer-most structural layer of mostmulti-layer fuel tanks includes HDPE, which is chemically not adhesiveto most, if not all, other materials, the inner-most structural layer 54of the overlay 18 is preferably composed of HDPE as well. This promotesadhesion or bonding between the overlay 18 and the fuel tank body 12 inthe presence of heat treatment or other adhesion promoting processes.The outer-most structural layer 52 of the overlay 18 may include anysuitable structural material. As an example, in the overlay 18 providedin FIG. 3, the outer layer 52 is made of polyethylene including afoaming or blowing agent. This material composition provides the overlay18 with some contact resistance to prevent tearing of the overlay 18 andfurther environmentally protects and structurally reinforces the seam 14to which the overlay 18 is applied.

Other representative examples of available multi-layer overlays that cansuitably be used in the method of the present invention include, withoutlimitation, three or five-layer configurations. Not inclusively, thepolymeric barrier layer 50 may be replaced by a metallic barrier stripor layer made of, for example, aluminum. A suitable multi-layer overlayaccording to one presently preferred implementation includes apolyester-polyethylene-aluminum-polyester-polyethylene five-layeroverlay commercially available from Unipac Corp. Other suitablemulti-layer overlays include apolyethylene-adhesive-EVOH-adhesive-polyethylene five-layer overlay, apolyethylene-adhesive-metal-adhesive-polyethylene five-layer overlay orother overlays of similar construction. Such multi-layer overlays areavailable as either a thin roll or as a wide sheet that can be cut intothe desired size and shape.

The choice between a polymeric barrier layer and a metallic barrierlayer can depend at least in part upon the method by which the overlay18 will be adhered to the fuel tank body 12. Overlays including apolymeric barrier layer may be adhered to the tank wall 26 by physicalheating methods, such as hot rolling, whereas overlays including ametallic barrier layer may be adhered to the tank body 12 by electricalheating methods, such as induction. These methods will later bediscussed in more detail.

Prior to sealing a weld or pinch seam formed in a multi-layer fuel tankbody, the seam can be assessed for rough edges that may have been formedduring a pinching or welding process. For example, a flash trim is oftenformed when forming a pinch seam between two halves of a fuel tank bodyor when pinching closed an end of a cylindrical extruded parison. Theflash trim can be a relatively sharp protrusion of polymeric materialthat follows all or at least one or more sections of the periphery ofthe pinch seam. This trim flash is undesirable because it may tear orslice the overlay when applied thereto, or inhibit close attachment ofthe overlay to the tank, thereby hindering and weakening the vapor seal.

To remove the trim flash and smooth the pinch seam 14, a pre-treatmentstep may be performed. One potential pre-treatment step includesapplying a flame from, for example, a flame torch to the flash trimalong the periphery of the pinch seam 14 until the flash trim is removedand the seam 14 is smooth. The flame may be applied continuously untilthe flash trim is removed or may be applied in cycles. Other non-smoothsurfaces, for example, formed from component weld seams may also betreated with the flame. Although optional, the advantage of using thepre-treatment process, besides smoothing the surfaces of the weld seamsfor better vapor sealing effect, includes further ionizing the HDPEsurface thereby making it slightly more adhesive. Thus, the HDPEinner-most structural layer 54 of the overlay 14 can be better attachedto the fuel tank wall 26 for better adhesion of the overlay 18 thereto.

Application of pressure and heat to the overlay 18 to achieve a goodvapor seal over a welded seam of a fuel tank, in accordance with onepresently preferred aspect of the present invention, can be achieved bya variety of different processes, some of which are shown in FIGS. 4-9.It should be appreciated that these processes are not inclusive andother processes may be employed. The processes shown in FIGS. 4-8 willbe described in sealing the pinch seam 14 whereas the process shown inFIG. 9 will be described in sealing an arbitrarily selected surface areaof the fuel tank body 12. Any one of the processes shown in FIGS. 4-9,however, may be used to seal any seam or any selected surface area onthe fuel tank body 12.

In applying the overlay to the fuel tank, the multi-layer overlay 18 isprepared by cutting a piece that will conform to the shape of the pinchseam 14 and is large enough to form an adequate hydrocarbon vapor seal.As shown in FIG. 4-6, the multi-layer overlay 18 may be applied to thetank wall 26 by press rolling the overlay 18 on the outer structurallayer 30 of the tank wall 26 in the presence of a heating device.Generally, for all of the disclosed processes and apparatus, the amountof heat to be administered to the overlay 18 to form a suitable seal isabout 200° C. to about 270° C. In reference to FIG. 3 in conjunctionwith FIGS. 4-6, an adhesive bond is formed between the structural layer54 of the overlay 18 and the structural layer 30 of the tank wall 26 andin all of the disclosed processes and apparatus is strengthened byapplying a pressure of at least 5 psi to the heated area to urge theoverlay into engagement with the structural layer.

As shown in FIG. 4, the overlay 18 preferably is adhered to the tankwall 26 by simultaneously applying heat and pressure to the top surface73 of the overlay 18 along the length of the pinch seam (not shown)using a high temperature roller 68. The high temperature roller 68supplies enough heat that will travel through the multiple layers of theoverlay 18 and effectively heat the inner-most structural layer (notshown) of the overlay 18 and the mating layer 30′, 30″ of the tank wallto a temperature in the range of about 200° C. to 270° C. A pressureroller 70 then follows the high temperature roller 68 to strengthen theadhesive bond between the overlay 18 and the outer structural layer 30of the tank wall 26. Alternatively, an adhesive bond may be formedbetween the overlay 18 and the tank wall 26 using two high temperaturerollers 68, where one roller heats the outer-most structural layer 30 ofthe tank wall 26 and the other roller heats the inner-most structurallayer (not shown) of the overlay 18, which is shown in FIG. 5, or thepre-treatment flame process as described above may supply enough heat tobond the overlay to the tank wall and only pressure need then be applied(not shown). For multi-layer overlays including a metallic barrierlayer, heat may be applied using induction heating and thus the heatingdevice may be an induction coil 72, as generally shown in FIG. 6.

Alternative bonding methods may be used in adhering the overlay 18 tothe tank wall 26 along a welded or pinched seam, examples of which areshown in FIGS. 7-8. As shown in FIG. 7, a pre-cut piece of overlay 18may be placed over the welded seam and a heated platen 74, which is aheated sheet of pre-formed geometry mimicking the shape of tank wall 26,may then be placed thereover. The heated platen 74 may operate as both aheating device and a pressure device for properly sealing the overlay 18along the weld seam 14.

As shown in FIG. 8, a pre-formed hotdrop manifold or a hot tip runner 77having a geometry mimicking the shape of the tank wall 26 may be placedover the overlay 18, preferably leaving a space 76 of a couplemillimeters between them. Relatively low pressure of about 50 psi from aplastic injection molding press 78 is applied to the overlay toinitially bond the overlay 18 to the outer-most structural layer 30 ofthe overlay wall 26. Then a molten plastic, preferably a polyethylenebased resin having a high melt flow property, is injected into thespace, which heats up the overlay and allows it to bond to the surfaceof the tank wall 26. The plastic layer remains on the surface of theoverlay 18, thereby providing a protective barrier or shield over theoverlay 18.

The multi-layer overlay 18 may also be adhered to the surface of thefuel tank wall 26 by molding, such as insert molding the overlay 18 tothe fuel tank during the fuel tank molding or forming process, where theoverlay 18 will act as an additional barrier layer to vapor permeationthrough the tank wall 26. As shown in FIG. 9, a sheet or piece 18′ ofthe multi-layer overlay is die-cut to a size that is just slightlysmaller than the top surface of the fuel tank body 12. The multi-layeroverlay 18′ is placed within a cavity 90 of a mold 92 against apre-determined desired surface, such as a bottom surface 94 of the moldcavity 90, and may be held in place, for example, by vacuum (not shown)or by any other suitable means. As shown in FIG. 9, the overlay 18 iscut to a desired size so that the overlay 18 covers the desired surfacearea of the tank body 12, as shown in FIG. 10, or in the cut-awayportion of the overlay 18′ disposed on the top surface of the tank body12, as shown in FIG. 1.

Alternatively, as shown in FIGS. 11 and 12, an overlay 18″ may beconcave or otherwise shaped to facilitate application of the overlay 18″to the corresponding portion of the fuel tank. The overlay 18, 18′, 18″may extend around or over one or more corners where the fuel tankbarrier layer may be further stretched as the tank is formed and hence,may be thinner than adjacent areas. The overlay 18, 18′, 18″ which mayinclude perforations to allow the release of air that may become trappedbetween the overlay and tank, may be molded to the tank body 12 duringthe vacuum forming, injection molding, blow molding, or other known fueltank molding or fuel tank forming process.

The overlay 18, 18′, 18″ may be formed with detailed or contouredsurface features to match the fuel tank shell and may further includeholes or cut-outs (not shown) for welding other fuel tank components tothe fuel tank, such as a filler pipe or other fuel module interfacecomponents. Also, the size and shape of the overlay 18, 18′, 18″ whetherflat or cup-shaped, may be varied to cover a variable amount of surfacearea of the fuel tank shell. The molded overlay 18 permits the coverageof larger surface areas of the tank body 12 with the same type ofpermeation reduction as would be experienced with pinch or componentweld seams, such as seams 14, 16 as shown in FIG. 1.

Component weld seams may also be sealed with a multi-layer overlay, asshown in FIG. 13. In reference to FIG. 13, the spout 24 comprises a neck82 and a flange 84, both of which are composed of polyethylene materialthat, in general, has low resistance to hydrocarbon vapor permeation. Acomponent weld seam 16 exists between a bottom surface 86 of the flange84 and outer-most structural layer 30 of the tank wall 26. As bettershown in FIG. 1, the multi-layer overlay 18 is die-cut into an annulardisc having a hole 87 (shown in FIG. 13) formed in its center that issized to receive the neck portion 82 of the spout 24. The disc comprisesa body 88 that is radially large enough to encircle the flange 84 of thespout 24. Using the same methods as described above, depending of courseupon the barrier material used in the multi-layer overlay, the overlay18 can be bonded or otherwise attached to the fuel tank to seal thecomponent weld seam 16. The overlay may also be used with othercomponents mounted on or carried by the fuel tank, including, forexample, vent valves and fuel pump modules which may have flanges thatoverlie and are coupled to the fuel tank. The overlay may also coverplugs or caps that close holes in the fuel tank, as well as anywhereelse desirable, including on or over tubes, pipes or other fittings in afuel system or associated with a fuel tank.

As previously mentioned, the multi-layer overlay 18 may be provided as aroll or as a sheet of material, as examples. For sealing straight-linedpinch seams, like pinch seam 14 shown in FIG. 1, the roll of overlayprovides relatively thin or flat strips of overlay material that willsuitably cover the pinch seam 14 and create a suitable hydrocarbon vaporseal. Sometimes, however, the fuel tank has a somewhat convoluted shapeand thus also has a convolutedly-shaped pinch seam 80, such as shown inFIG. 14. Application of the straight-edge multi-layer overlay providedin the roll to the convolutedly-shaped pinch seam 80 will pose somedifficulties. In such cases, the overlay 14 may be obtained as a sheetrather than as a roll and the sheet may then be die-cut to the desiredshape of the seam 80 for proper coverage of the area to be sealed. Thisis also true for sealing component weld seams, which are commonlycircular in shape, such as the component weld seam 16 formed by weldingthe spout 24 to the tank body 12 shown in FIGS. 1 and 13. This also istrue for sealing surface areas of the tank body 12 using either arelatively flat overlay 18′ as shown in FIG. 9 or a shaped or contouredoverlay 18″ as shown in FIG. 11.

Accordingly, permeation windows often formed in pinch or weld seamsformed in multi-layer polymeric fuel tanks can be covered by amulti-layer overlay or substrate that spans any gaps in adjacent barrierlayers in the area of the seams to prevent or reduce hydrocarbon vaporpermeation through the fuel tank. Also, the fuel tank body 12 may becovered with a large piece of the overlay 18 to provide an additionalbarrier to vapor permeation through the tank wall 26. The method may beperformed with commercially available materials and is relativelyinexpensive to carry out.

While the forms of the invention herein disclosed constitute presentlypreferred embodiments, many others are possible. It is not intendedherein to mention all the possible equivalent forms or ramifications ofthe invention. For example, the term “overlay” is not intended to belimited to an overlay or sheet and furthermore is not intended to belimited to disposal on the exterior surfaces of the tank wall but mayalso be disposed on interior surfaces of the tank wall as well. It isunderstood that terms used herein are merely descriptive, rather thanlimiting, and that various changes may be made without departing fromthe spirit and scope of the invention as defined by the followingclaims.

The invention claimed is:
 1. A method of reducing fuel vapor permeationthrough a polymeric multi-layer fuel tank comprising: forming amulti-layer polymeric fuel tank having a wall defining an enclosure inwhich a hydrocarbon fuel is stored with the wall having a hydrocarbonfuel vapor permeation barrier layer which is discontinuous at a seam andat least one polymeric structural layer outboard of and adhered to thebarrier layer; providing a separate overlay having a hydrocarbon fuelvapor permeation barrier layer of a polymeric or metal materialresistant to hydrocarbon fuel vapor permeation therethrough and at leastone polymeric structural layer adhered to the barrier layer throughoutthe barrier layer of the overlay; disposing the overlay over at least aportion of the seam, discontinuous barrier layer and outer structurallayer of the wall; heating to a temperature of at least about 200° C.the structural layer of the overlay and a confronting portion of thestructural layer of the wall; and applying pressure of at least 5 psi tourge into engagement the heated structural layer of the overlay and theconfronting heated portion of the structural layer of the wall to adhereand bond them together throughout the structural layer of the overlay.2. The method of claim 1 wherein the overlay comprises polymeric innerand outer structural layers with the barrier layer disposed between andadhered to the inner and outer structural layers throughout the barrierlayer of the overlay.
 3. The method of claim 1 wherein the barrier layerof the overlay is an EVOH polymeric material.
 4. The method of claim 1wherein the barrier layer of the overlay is a metal material.
 5. Themethod of claim 1 further comprising molding the structural layer of theoverlay to at least a portion of the polymeric structural layer of thewall of the multi-layer tank during forming of the fuel tank.
 6. Themethod of claim 1 wherein the structural layer of the overlay and theadjoining portion of the structural layer of the wall are heated to atemperature of about 200° C. to 270° C.